1. Field of the Invention
The present invention relates to a semiconductor memory device and, in particular, to a cell plate line driver circuit which can implement a strong drive power and rapid operability required in case of designing a RAM having a material of large electrostatic capacity as a memory device and a circuit for transferring an output of the cell plate line driver circuit to a cell plate line without loss.
2. Related prior art
A driver for driving a word line for controlling an In/Out of information in a memory device of DRAM memory semiconductor which is presently commercially available requires only a potential higher than or equal to a certain level.
Therefore, the word line driver plays a role of making ON/OFF the potential higher than or equal to the certain level and comprises, as shown in FIG. 1 a level shifter section 10 for shifting a voltage level, a driver section 30 for driving the output voltage of the level shifter section 10 to a word line, and a control section 40 for controlling the operation of the driver section 30.
In operation of the word line driver constituted as described above, when a control signal C1 applied to the control section 40 is enabled with a value "High", it turns on a N-MOS transistor N31 of the driver section 30 via each inverter INV41, 42 in the control section.
on the other hand, the control signal C1 is input to the level shifter section 10 via a delay 50 having a predetermined delay time, and thereafter operates the level shifter so as to apply a high voltage Vpp to the driver section 30 via a PMOS transistor P11, and eventually this voltage is applied to the word line.
FIG. 2 shows a voltage variation of each line varying in a process in which the above described operation is performed, and it can be seem from the drawing that the word line W/L gradually increases in its voltage to Vpp.
The word line driver operating as described above has small electrostatic capacity of memory device presently manufactured with silicon, and therefore, the driving capability of the driver is not very important.
However, when using a material of large electrostatic capacity including a ferroelectric materials instead of silicon which is a memory device of DRAM, in case of using a conventionally used word line driver structure as they are to a cell plate line drive, various problems occur.
In case of using the ferroelectric materials as a memory device, a certain level is required to the cell plate line.
In case of using the material of large electrostatic capacity as a memory device, since the material itself has very large electrostatic capacity in comparison to the silicon, it requires a strong driving capability.
Therefore, to commercialize a RAM using such material as a memory device, the word line driver circuit presently used in DRAM can not be used and new type of circuit is required.